1. Field of the Invention
The invention relates to electrical power conversion and more particularly to an improved control circuit for a high frequency resonant converter for transferring electrical power between first and second power terminals.
2. Information Disclosure Statement
In the last two decades, substantial progress has been made in electrical converters for transferring one form of electrical energy into a more useable form of electrical energy. Electrical converters have many applications such as motor controllers, the generation and transmission of electric energy, and various power supplies with low specific weight and volume.
Among the many methods of providing power conversion is the series resonant converter. In the series resonant converter, a DC or an AC input is applied through a semiconductor switching network to a series resonant circuit. The output of the series resonant circuit may be connected to a load through a second semiconductor switching network. The series resonant circuit oscillates at a high frequency typically 10 KHz. to 50 KHz. enabling the series resonant circuit to provide low specific weight and volume. Furthermore, the series resonant circuit provides natural current commutation of the semiconductor switching network or networks. Accordingly, the series resonant circuit provides an improved reliability due to the moderate stresses applied during switching of the semiconductor switches under zero current conditions.
Another advantage of the series resonant converter resides in the high internal resonant frequency which avoids the interposition of low frequency filters in the signal processing. The high frequency components generated by the series resonant converter can be inhibited from entering the source or the load by applying moderately sized high frequency filters.
Still a further advantage of the series resonant converter is found in the fast response and accurate control due to the high internal resonant frequency of the series resonant converter.
Various control circuits have been proposed in the prior art for improving the control, the power rating and the reliability of the basic series resonant converter. In addition, many circuits have been proposed in the prior art for enabling the output of single or multiphase AC waveform at a variable frequency output. However, none in the prior art have proposed a control system for a series resonant converter to the degree established by the present invention.
Therefore, it is an object of the present invention to provide an improved control circuit for a resonant converter for shaping each resonant current waveform independently of the load impedance and the polarity and magnitude of the output voltage.
Another object of the present invention is to provide an improved control circuit for a resonant converter for generating low distortion single phase or multiphase AC waveforms with bidirectional power flow from a two terminal DC or a multiterminal AC source of electrical energy.
Another object of the present invention is to provide an improved control circuit for a resonant converter capable of adapting to changes in the dynamics of the electrical source and/or the electrical load to insure the proper operating conditions for the resonant circuit.
Another object of the present invention is to provide an improved control circuit for a resonant converter capable of limiting the stored energy in the resonant circuit for normal and abnormal operating conditions of the resonant converter.
Another object of the present invention is to provide an improved control circuit for a resonant converter capable of quantizing the energy stored in a capacitor of the resonant circuit for each resonant cycle during normal and abnormal operating conditions of the resonant converter.
Another object of the present invention is to provide an improved control circuit for a resonant converter having power transfer control means for selectively actuating switch means to selectively initiate resonant pulses in the resonant circuit of the resonant converter for transferring electrical power between a source and a load.
Another object of the present invention is to provide an improved control circuit for a resonant converter having sensor means for instantaneously monitoring the voltage at the source and the load and the voltage and current in the resonant circuit to enable a predictor circuit to instantaneously and continuously predict prior to the completion of each of the resonant pulses when the initiation of conduction of the switch means will produce a resonant pulse having a final waveform in conformity with a pre-established standard.
Another object of the present invention is to provide an improved control circuit for a resonant converter capable of initiating conduction of the switch means within each resonant pulse to conform each resonant pulse to a pre-established standard and to quantize the energy stored in the capacitor of the series resonant circuit.
Another object of the present invention is to provide an improved control circuit for a resonant converter capable of applying the concepts of recurrent instantaneous forward or reverse power flow independent of the conversion ratio q=u.sub.o /e.sub.s of the resonant converter.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention is a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.